Gas sensor element and gas sensor

Abstract

A gas sensor element includes a solid electrolyte body having oxygen ion conductivity, a measurement electrode provided on one surface of the solid electrolyte body and exposed to a measurement gas, and a reference electrode provided on the other surface of the solid electrolyte body and exposed to a reference gas. Both the measurement electrode and the reference electrode include noble metal particles, solid electrolyte particles having oxygen ion conductivity, and pores. The measurement electrode comprises a surface measurement electrode layer comprising a surface serving as a contact surface with the measurement gas and an intermediate measurement electrode layer disposed in contact with a surface at solid electrolyte body side of the surface measurement electrode layer. The surface measurement electrode layer has a higher porosity than the intermediate measurement electrode layer has. The gas sensor comprises the gas sensor element.

What is claimed is: 
     
       1. A gas sensor element comprising:
 a solid electrolyte body having oxygen ion conductivity, a measurement electrode provided on a first surface of the solid electrolyte body and exposed to a measurement gas, and a reference electrode provided on a second surface of the solid electrolyte body that is opposite to the first surface and exposed to a reference gas, wherein 
 both the measurement electrode and the reference electrode comprise noble metal particles, solid electrolyte particles having oxygen ion conductivity, and pores, and 
 the measurement electrode comprises: 
 a surface measurement electrode layer comprising a surface serving as a contact surface with the measurement gas and an intermediate measurement electrode layer comprising a plurality of layers, one layer of the intermediate measurement electrode layer being disposed in contact with a surface at a solid electrolyte body side of the surface measurement electrode layer, and 
 the surface measurement electrode layer has a higher porosity than porosity of each of the plurality of layers of the intermediate measurement electrode layer, and 
 each of the plurality of layers included in the intermediate measurement electrode layer have a porosity increasing from the solid electrolyte body toward the surface measurement electrode layer. 
 
     
     
       2. The gas sensor element according to  claim 1 , wherein
 the surface measurement electrode layer has a porosity of 15% or more and 30% or less. 
 
     
     
       3. The gas sensor element according to  claim 1 , wherein
 each of layers of the intermediate measurement electrode layer has a porosity of 15% or less. 
 
     
     
       4. The gas sensor element according to  claim 1 , wherein
 the reference electrode comprises: 
 a surface measurement electrode layer comprising a surface serving as a contact surface with the reference gas and an intermediate measurement electrode layer disposed in contact with a surface at a solid electrolyte body side of the surface measurement electrode layer of the reference electrode, and 
 the surface measurement electrode layer of the reference electrode has a higher porosity than the intermediate measurement electrode layer of the reference electrode. 
 
     
     
       5. The gas sensor element according to  claim 4 , wherein
 the surface measurement electrode layer of the reference electrode has a porosity of 15% or more and 30% or less. 
 
     
     
       6. The gas sensor element according to  claim 4 , wherein
 the intermediate measurement electrode layer of the reference electrode has a porosity of 15% or less. 
 
     
     
       7. The gas sensor element according to  claim 4 , wherein
 the intermediate measurement electrode layer of the reference electrode comprises a plurality of layers. 
 
     
     
       8. The gas sensor element according to  claim 1 , wherein
 the noble metal particles comprise Pt or an alloy of Pt and at least one type selected from a group consisting of Rh, Pd, Au, and Ag. 
 
     
     
       9. A gas sensor comprising the gas sensor element according to  claim 1 .